I will purify HMG-CoA reductase from rats killed at the time of the nadir of the diurnal rhythm. The properties of this enzyme will be compared to those of enzyme purified from animals killed at the peak of the rhythm and fed either a normal diet or a diet supplemented with cholestyramine. I will prepare antibodies to the purified reductase and use the antibodies to study enzyme turnover in isolated rat hepatocytes and intact rats.